<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
<script>

const tree = {
    val: 'a',
    children: [
        {
            val: 'b',
            children: [
                {
                    val: 'd',
                    children: [],
                },
                {
                    val: 'e',
                    children: [],
                }
            ],
        },
        {
            val: 'c',
            children: [
                {
                    val: 'f',
                    children: [],
                },
                {
                    val: 'g',
                    children: [],
                }
            ],
        }
    ],
};

function bfs() {
    let q = []
    q.push(tree)
    while(q.length){
        let n = q.shift()
        console.log(n.val)
        n.children.forEach((item) => {
            q.push(item)
        })
    }
}

bfs()


</script>
</body>
</html>